1. Field of the Invention
The disclosed technology relates to low voltage drop unidirectional smart bypass elements, and more particularly, although not exclusively, concerned with unidirectional bypass elements for use in photovoltaic panel solar modules to provide a current bypass in the event of suspension of operation of at least one photovoltaic solar cell in such modules.
2. Description of the Related Technology
Large-area photovoltaic (PV) panels tend to be composed of multiple individual solar cells connected in series to deliver a large amount of electrical power to the load. Arranging the solar cells in series allows the energy transfer to be accomplished at low current levels and at a relative high voltage level, thereby minimizing the power losses in the power lines. This configuration works very well provided that all solar cells are receiving the same amount of optical energy, namely, all solar cells contribute equally to the overall power conversion. However, in the case when one solar cell in the module starts receiving less optical energy because it is temporarily in the shade or because its surface has become dirty, the current in the series connection of all solar cells will be limited by this “failing” cell. As a result, not only the power of the “failing” cell itself is lost, but also the power generation of the working solar cells is dramatically reduced. In the case where the current of the failing solar cell drops to zero, the power conversion is completely suspended and the whole solar module in the PV panel becomes non-functioning. Furthermore, the voltage from the functioning cells will be placed in reverse over this “failing” cell. If this voltage is greater than the breakdown voltage of this cell, it will break down dissipating the power generated by the other cells and creating a local hot spot. Such breakdown may permanently damage the PV panel.
US-A-2009/0184746 describes a low voltage drop unidirectional electronically-controlled switch for use with a solar or PV panel to bypass a “failing” cell by blocking current flow when the electronic switch is open and to pass current when the electronically-controlled switch is closed. The electronically-controlled switch is controlled by a control circuit and is refreshed periodically. The electronically-controlled switch is implemented by a pair of reverse serially connected field effect transistors (FETs), such as NMOSFET devices, the drain of each of the serially connected FET devices forming the terminals of the electronically-controlled switch. The control circuit refreshes the operational status of the electronically-controlled switch to ensure that the switch is closed only for the shortest time possible, for example, in the case of the PV panel acting as a “failing” cell due to the traverse of a cloud over the sun which blocks the generation of current for a given period of time.
However, the power dissipated when one or more solar cells is bypassed is substantial, and the operation of the PV solar panel becomes less efficient. Moreover, the power lost to the system is emitted as heat, which determines thermal considerations in the PV solar panel layout, the design of the electronically-controlled switch and ultimately the cost of the arrangement.